Proprotein convertase subtilisin-kexin type 9 (hereinafter called “PCSK9”), also known as neural apoptosis-regulated convertase 1 (“NARC-I”), is a proteinase K-like subtilase identified as the 9th member of the mammalian PCSK family; see Seidah et al, 2003 PNAS 100:928-933. The gene for PCSK9 localizes to human chromosome 1p33-p34.3. PCSK9 is expressed in cells capable of proliferation and differentiation including, for example, hepatocytes, kidney mesenchymal cells, intestinal ileum, and colon epithelia as well as embryonic brain telencephalon neurons.
Original synthesis of PCSK9 is in the form of an inactive enzyme precursor, or zymogen, of ˜72-kDa which undergoes autocatalytic, intramolecular processing in the endoplasmic reticulum (“ER”) to activate its functionality. The gene sequence for human PCSK9, which is ˜22-kb long with 12 exons encoding a 692 amino acid protein, can be found, for example, at Deposit No. NP_777596.2. Human, mouse and rat PCSK9 nucleic acid sequences have been deposited; see, e.g., GenBank Accession Nos.: AX127530 (also AX207686), AX207688, and AX207690, respectively.
Human PCSK9 is a secreted protein expressed primarily in the kidneys, liver and intestines. It has three domains: an inhibitory pro-domain (amino acids 1-152; including a signal sequence at amino acids 1-30), a catalytic domain (amino acids 153-448), and a C-terminal domain 210 residues in length (amino acids 449-692), which is rich in cysteine residues. PCSK9 is synthesized as a zymogen that undergoes autocatalytic cleavage between the pro-domain and catalytic domain in the endoplasmic reticulum. The pro-domain remains bound to the mature protein after cleavage, and the complex is secreted. The cysteine-rich domain may play a role analogous to the P-(processing) domains of other Furin/Kexin/Subtilisin-like serine proteases, which appear to be essential for folding and regulation of the activated protease. Mutations in PCSK9 are associated with abnormal levels of low density lipoprotein cholesterol (LDL-c) in the blood plasma (Horton et al., 2006 Trends. Biochem. Sci. 32(2):71-77).
PCSK9 has been ascribed a role in the differentiation of hepatic and neuronal cells (Seidah et al, supra), is highly expressed in embryonic liver, and has been strongly implicated in cholesterol homeostasis.
The identification of compounds and/or agents effective in the treatment of cardiovascular affliction is highly desirable. Reductions in LDL cholesterol levels have already demonstrated in clinical trials to be directly related to the rate of coronary events; Law et al, 2003 BMJ 326: 1423-1427. More, recently moderate lifelong reduction in plasma LDL cholesterol levels has been shown to be substantially correlated with a substantial reduction in the incidence of coronary events; Cohen et al, supra. This was found to be the case even in populations with a high prevalence of non-lipid-related cardiovascular risk factors; supra.
Accordingly, it is of great importance to identify therapeutic agent permitting the control of LDL cholesterol levels.
Accordingly, it would be of great importance to produce a medicament that inhibits or antagonizes the activity of PCSK9 and the corresponding role PCSK9 plays in various therapeutic conditions.
Expression or upregulation of PCSK9 is associated with increased plasma levels of LDL cholesterol, and inhibition or the lack of expression of PCSK9 is associated with low LDL cholesterol plasma levels. Significantly, lower levels of LDL cholesterol associated with sequence variations in PCSK9 have conferred protection against coronary heart disease; Cohen, 2006 N. Engl. J. Med. 354: 1264-1272.